linux-kernel - [PATCH 1/2] mfd: mfd-core: Add mechanism for removal of a subset of children

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Date:   Mon, 11 May 2020 16:53:32 +0100
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     <lee.jones@...aro.org>
CC:     <broonie@...nel.org>, <patches@...nsource.cirrus.com>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH 1/2] mfd: mfd-core: Add mechanism for removal of a subset of children

Currently, the only way to remove MFD children is with a call to
mfd_remove_devices, which will remove all the children. Under
some circumstances it is useful to remove only a subset of the
child devices. For example if some additional clean up is required
between removal of certain child devices.

To accomplish this a tag field is added to mfd_cell, and a
corresponding mfd_remove_devices_by_tag function is added to
remove children with a specific tag. This allows a good amount of
flexibility in which child devices a driver wishes to remove, as a
driver could target specific drivers or a large group. Allowing other
use-cases such as removing drivers for functionality that is no longer
required.

Some investigation was done of using the mfd_cell name and id fields,
but it is hard to achieve a good level of flexibility there, at least
without significant complexity. Since the id gets modified by the core
and can even by automatically generated. Using the name alone would
work for my usecase but it is not hard to imagine a situation where it
wouldn't.

Signed-off-by: Charles Keepax <ckeepax@...nsource.cirrus.com>
---

Following on from our discussions here:

https://lore.kernel.org/lkml/20200122110842.10702-2-ckeepax@opensource.cirrus.com/#t

Happy to discuss other approaches as well, but this one was quite
appealing as it was very simple but affords quite a lot of flexibility.

Thanks,
Charles

 drivers/mfd/mfd-core.c   | 11 +++++++++++
 include/linux/mfd/core.h |  2 ++
 2 files changed, 13 insertions(+)

diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
index f5a73af60dd40..83a57186169de 100644
--- a/drivers/mfd/mfd-core.c
+++ b/drivers/mfd/mfd-core.c
@@ -287,6 +287,7 @@ static int mfd_remove_devices_fn(struct device *dev, void *data)
 {
 	struct platform_device *pdev;
 	const struct mfd_cell *cell;
+	int tag = (int)data;

 	if (dev->type != &mfd_dev_type)
 		return 0;
@@ -294,6 +295,9 @@ static int mfd_remove_devices_fn(struct device *dev, void *data)
 	pdev = to_platform_device(dev);
 	cell = mfd_get_cell(pdev);

+	if (tag && cell->tag != tag)
+		return 0;
+
 	regulator_bulk_unregister_supply_alias(dev, cell->parent_supplies,
 					       cell->num_parent_supplies);

@@ -301,6 +305,13 @@ static int mfd_remove_devices_fn(struct device *dev, void *data)
 	return 0;
 }

+void mfd_remove_devices_by_tag(struct device *parent, int tag)
+{
+	device_for_each_child_reverse(parent, (void *)tag,
+				      mfd_remove_devices_fn);
+}
+EXPORT_SYMBOL(mfd_remove_devices_by_tag);
+
 void mfd_remove_devices(struct device *parent)
 {
 	device_for_each_child_reverse(parent, NULL, mfd_remove_devices_fn);
diff --git a/include/linux/mfd/core.h b/include/linux/mfd/core.h
index d01d1299e49dc..f68d668b2cb7c 100644
--- a/include/linux/mfd/core.h
+++ b/include/linux/mfd/core.h
@@ -58,6 +58,7 @@ struct mfd_cell_acpi_match {
 struct mfd_cell {
 	const char		*name;
 	int			id;
+	int			tag;

 	int			(*enable)(struct platform_device *dev);
 	int			(*disable)(struct platform_device *dev);
@@ -135,6 +136,7 @@ static inline int mfd_add_hotplug_devices(struct device *parent,
 }

 extern void mfd_remove_devices(struct device *parent);
+extern void mfd_remove_devices_by_tag(struct device *parent, int tag);

 extern int devm_mfd_add_devices(struct device *dev, int id,
 				const struct mfd_cell *cells, int n_devs,
-- 
2.11.0